In the subset of unconventional natural gases, shale gas, tight gas and coal bed methane are now being produced to some extent, whereas the biggest part of the unconventional resource is made up of gas hydrates which are still in the exploratory phase of development. It is recognised that the resource potential of gas hydrates existing in the Earth is twice the amount of the combined remaining resources of other fossil fuels (i.e. coal, oil and natural gas). So far, hydrates have been recovered using pressure coring carried out by vessels using conventional drilling methods. Original attempts to recover hydrates were based on upgrading underwater drill rigs with autoclaves. The present paper reviews the importance of pressure coring systems with the objective of assisting researchers and engineers in the development of technologies that will support the exploration of gas hydrates and to consider underwater drill rigs as novel drilling tools.